Subject:
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Re: A robot who knows his position (fwd)
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 30 Apr 1999 14:02:06 GMT
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Viewed:
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955 times
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In lugnet.robotics, Mario Ferrari writes:
> In lugnet.robotics, Mike Moran writes: • [ ... ]
> > For my next robot I'm going to abandon dead reckoning (at least on it's own)
> > in favour of some external sensing relative to a landmark.
>
> Dead-reckoning should be used BETWEEN two consecutive (artificial) landmark
> sensing. When you get any external reference point you can zero your
> accumulated errors.
Well, I know this, I was just seeing how far I could get without landmarks.
An idea Richard Franks and I had was to use black and white approx. A4 size
printed markers. These markers would contain a pattern that was detectable by a
down-facing light-sensor. When the robot got "lost" ie after a predefined
number of moves, or after it's estimated error became too much, it would go
into "wander" mode until it found a marker. Once it had worked out which marker
it was at, it would consult an internal map of predefined marker positions
(which it had been told) and then continue from there. Unfortunately, this
relied on fairly accurate dead reckoning to allow it wander around before
getting lost.
>
> > My flatmate has
> > informed me of a way the Chinese used to navigate before they had compasses.
> > Basically, you get a two wheeled vehicle, take the output of each wheel and
> > feed it into a differential such the differential is still when they are • moving
> > in the same direction. Take the output of the diff. and arrange it so that it
> > makes an arrow sticking out of the top of the contraption (think "weather
> > vane") turn. Down-gear this turning a bit. The result of this is the fact • that
> > when you move the vehicle around, the "arrow" always stays pointing in a
> > direction parallel to it's original direction. I reckon you could use this
> > effect to tie into something external. Don't ask me what just yet ;-)
>
> Seems interesting. But you would still have problem with slippage...
Probably. It also relies on both wheels bieng in contact with the ground at any
time. However, I was considering resetting it every so often via a more
permanent landmark. After watching a trailer which implemented the "Chinamens
compass" bieng trailed around behind my current robot for a while, I came to
the conclusion that it was *fairly* accurate ie to within maybe 10 or so
degrees. This sounds pretty bad, but it's a lot better than I've gotten (or
estimated) via other means.
> I think a magnetic or gyro compass would work better. Is there anybody around
> who did interface a compass to the RCX?
I did consider trying to rig up a crude light-sensor looking at a cheap
compass, but thought against it. Just detecting the, usually red and blue,
arrow sounds pointless, whilst taking one apart and attaching a patterned disk
to it seems infeasible as the card of the disk would probably be too heavy for
the compass needle to move around. Is this the only way to do this without
building some sort of little bit of electronics gadgetry?
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Message has 1 Reply:
 | | Re: A robot who knows his position (fwd)
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| (...) [snip] (...) I'm currently looking at an RCX interface to a Dinsmore compass module that uses Hall-Effect sensors to detect N-S-E-W and triggers two of them when dead-center between two cardinal points, so you get N-NE-E-SE... Not that great (...) (25 years ago, 30-Apr-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: A robot who knows his position (fwd)
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| (...) Looking forward to seeing them :) (...) Dead-reckoning should be used BETWEEN two consecutive (artificial) landmark sensing. When you get any external reference point you can zero your accumulated errors. (...) moving (...) Seems interesting. (...) (25 years ago, 28-Apr-99, to lugnet.robotics)
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